{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,15]],"date-time":"2026-10-15T16:03:54Z","timestamp":1792080234061,"version":"4.4.0"},"reference-count":27,"publisher":"Wiley","issue":"4","license":[{"start":{"date-parts":[[2026,3,30]],"date-time":"2026-03-30T00:00:00Z","timestamp":1774828800000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"},{"start":{"date-parts":[[2026,3,30]],"date-time":"2026-03-30T00:00:00Z","timestamp":1774828800000},"content-version":"tdm","delay-in-days":0,"URL":"http:\/\/doi.wiley.com\/10.1002\/tdm_license_1.1"}],"content-domain":{"domain":["aapm.onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["Medical Physics"],"published-print":{"date-parts":[[2026,4]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>The van Herk margin formula, derived for 3\u2010D conformal radiotherapy with a uniform 3.2 mm dose penumbra and no intrinsic dose buffer, remains widely used to design CTV\u2010to\u2010PTV expansions in contemporary image\u2010guided prostate radiotherapy. However, coplanar VMAT techniques often feature broader penumbrae and explicit PTV\u2013isodose clearances, potentially violating the assumptions underlying the original formulation and leading to overly conservative margins.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Purpose<\/jats:title>\n                    <jats:p>We investigated whether the widely adopted van Herk margin formula overestimates clinical target volume (CTV)\u2010to\u2010planning target volume (PTV) expansions for contemporary coplanar volumetric modulated arc therapy (VMAT) prostate treatments.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>Fifty consecutive intact\u2010prostate VMAT radiotherapy plans (two coplanar arcs; clinical margins 3 mm, except for 2 mm posterior) were exported. Direction\u2010specific 90% isodose\u2013to\u2010PTV gaps and penumbra widths were measured. Candidate anisotropic margins were tested by eroding the PTV to create CTV_eval. Monte\u2010Carlo simulations combined systematic (\u03a3) shifts with Gaussian random (\u03c3\u2032) blurring kernels of 0\u20132 mm were performed. Acceptability criteria of (i) CTV Dmin0.03 cc \u2265 90% Rx in \u2265 90% of simulated scenarios or (ii) population tumor\u2010control probability (TCP) loss &lt; 1 % were used.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>VMAT plans exhibited intrinsic 90% isodose clearances of 3\u20135 mm laterally\/anteriorly and 1\u20132 mm superior\u2013inferiorly, while axial\u2010plane penumbras were up to fivefold broader than van Herk's assumption. With a [0, 0, 2] mm (LR\/AP\/SI) margin, \u2265 90% of patients maintained Dmin0.03 cc \u2265 90% Rx provided \u03a3 lay within an ellipsoid of [2.0, 1.5, 1.8] mm and \u03c3\u2032 \u2264 [1.5, 2.0, 1.5] mm. Under TCP criteria the safe \u03a3 ellipsoid for high\u2010risk disease was [2.5, 1.9, 2.2] mm, while low\u2010intermediate risk was even less sensitive.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusions<\/jats:title>\n                    <jats:p>For image\u2010guided coplanar VMAT prostate radiotherapy, an anisotropic [0, 0, 2] mm CTV\u2010to\u2010PTV margin is sufficient for target coverage. A modified margin expression that subtracts the measured isodose\u2013to\u2010PTV gap and uses reduced random\u2010error coefficients better reflects modern practice.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1002\/mp.70415","type":"journal-article","created":{"date-parts":[[2026,3,31]],"date-time":"2026-03-31T01:23:24Z","timestamp":1774920204000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Monte Carlo\u2013based optimization of CTV\u2010to\u2010PTV margins for image\u2010guided VMAT prostate radiotherapy"],"prefix":"10.1002","volume":"53","author":[{"given":"Quan","family":"Chen","sequence":"first","affiliation":[{"name":"Department of Radiation Oncology Mayo Clinic Arizona  Phoenix Arizona USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ali","family":"Ammar","sequence":"additional","affiliation":[{"name":"Department of Radiation Oncology Mayo Clinic Arizona  Phoenix Arizona 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